Re: [ceph-users] rbd feature overheads
On Tue, Feb 13, 2018 at 1:24 AM, Blair Bethwaitewrote: > Thanks Ilya, > > We can probably handle ~6.2MB for a 100TB volume. Is it reasonable to expect > a librbd client such as QEMU to only hold one object-map per guest? Yes, I think so. Thanks, Ilya ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] rbd feature overheads
Thanks Ilya, We can probably handle ~6.2MB for a 100TB volume. Is it reasonable to expect a librbd client such as QEMU to only hold one object-map per guest? Cheers, On 12 February 2018 at 21:01, Ilya Dryomovwrote: > On Mon, Feb 12, 2018 at 6:25 AM, Blair Bethwaite > wrote: > > Hi all, > > > > Wondering if anyone can clarify whether there are any significant > overheads > > from rbd features like object-map, fast-diff, etc. I'm interested in both > > performance overheads from a latency and space perspective, e.g., can > > object-map be sanely deployed on a 100TB volume or does the client try to > > read the whole thing into memory...? > > Yes, it does. Enabling object-map on images larger than 1PB isn't > allowed for exactly that reason. The memory overhead is 2 bits per > object, i.e. 64K per 1TB assuming the default object size. > > object-map also depends on exclusive-lock, which is bad for use cases > where sharing the same image between multiple clients is a requirement. > > Once object-map is enabled, fast-diff is virtually no overhead. > > Thanks, > > Ilya > -- Cheers, ~Blairo ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
Re: [ceph-users] rbd feature overheads
On Mon, Feb 12, 2018 at 6:25 AM, Blair Bethwaitewrote: > Hi all, > > Wondering if anyone can clarify whether there are any significant overheads > from rbd features like object-map, fast-diff, etc. I'm interested in both > performance overheads from a latency and space perspective, e.g., can > object-map be sanely deployed on a 100TB volume or does the client try to > read the whole thing into memory...? Yes, it does. Enabling object-map on images larger than 1PB isn't allowed for exactly that reason. The memory overhead is 2 bits per object, i.e. 64K per 1TB assuming the default object size. object-map also depends on exclusive-lock, which is bad for use cases where sharing the same image between multiple clients is a requirement. Once object-map is enabled, fast-diff is virtually no overhead. Thanks, Ilya ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
[ceph-users] rbd feature overheads
Hi all, Wondering if anyone can clarify whether there are any significant overheads from rbd features like object-map, fast-diff, etc. I'm interested in both performance overheads from a latency and space perspective, e.g., can object-map be sanely deployed on a 100TB volume or does the client try to read the whole thing into memory...? -- Cheers, ~Blairo ___ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com